Process for the sensitization of photoconductors



United States Patent 3,287,116 PROCESS FOR THE SENSITIZATION OF PHOTOCONDUCTORS Helmut Hoegl, Geneva, Switzerland, assignor, by

34 Claims. (Cl. 96-1) This application is a division of copending application Serial No. 125,984, filed July 24, 1961, now abandoned, which, in turn, is a continuation-in-part of application Serial No. 30,752, filed May 23, 1960, and also now abandoned.

Electrophotographic material normally consists of a support on which there is a photoconductive substance, this coating being provided in the absence of light with an electrostatic charge. Then, the material is exposed to light behind a master, or an episcopic image is projected thereon, so that an electrostatic image is formed which corresponds to the master. This image is developed by being briefly contacted with a resin powder, whereupon a visible image is formed which is fixed by heating or by the action of solvents. In this way, an image of the master which is resistant to abrasion is obtained electrophotographically.

In the electrophotographic process as described an increase in the sensitivity of the photoconductive coatings has already been attempted by the addition of organic dyestuifs, e.g. triphenylmethane, Xanthene, phthalein, thiazine and acridine dyestutfs, to the photoconductors.

The absorption maxima of the organic photoconductors are mostly in the ultra-violet region of the spectrum. The addition of these dyestufi sensitizers achieves the result that the photoconductors become sensitive to visible light. Generally, the dyestutf sensitizers cause a displacement of the available sensitivity from the ultraviolet region to the visible region. With increased addition of dyestuff sensitizer, the sensitivity to visible light at first increases rapidly, but further additions give an increase in sensitivity which is much less than would be expected, and still further additions finally give no appreciable increase in sensitivity. The dyestuif sensitizers have the disadvantage that they color the coating considerably. In practice, the maximum achievable increase in sensitivity can seldom be utilized because then the photoconductor coatings have an intensity of color that is undesirable. Colorless or practically colorless photoconductor coatings are desired, since colored material can be employed only in special cases. If additions of dyestuff sensitizers are such as not to adversely aifect the coloring of the coating for practical purposes, the sensitizing eifect often does not meet the demands of general usage. Further, the dyestuff sensitizers have the disadvantage that they bleach out relatively quickly so that their sensitizing action tends to be lost during the storage of the electrophotographic material.

A process for the sensitization of photoconductor coatings has now been found in which organic substances, containing polarizing residues and being capable of serving as electron-acceptors in a molecule complex, having low molecular weight, i.e. being non-resinous, being colorless or of pale color and having a melting point above room temperature, are added to the photoconductor "ice cule complexes of the donor/acceptor type (known as 1r-complex) and contain at least one aromatic or heterocyclic ring, which may be substituted. Such photoconductors include aromatic hydrocarbons such as naphthalene, anthracene, benzanthrene, chrysene, p-diphenylbenzene, diphenyl anthracene, p-terphenyl, p-quaterphenyl, sexiphenyl; heterocycles such as N-alkyl carbazole, thiodiphenylamine, oxadiazoles, e.g., 2,5-bis-(p-aminophenyl)-1,3,4-oxadiazole and its N-alkyl and N-acyl derivatives; triazoles such as 2,5 bis-(p-aminophenyl)- l,3 ,4-triaz0le and its N-alkyl and N-acyl derivatives; imidazolones and imidazolthiones, e.g., 1,3,4,5-tetraphenyl-imidazolone-2 and 1,3,4,S-tetraphenyl-imidazolthione-Z; N-aryl-pyrazolines, e.g. 1,3,5-triphenyl-pyrazoline; hydrated imidazoles, e.g., 1,3-diphenyl-tetrahydroimidazole; oxazole derivates such as 2,5-diphenyloxazole-2- p-dimethylamino-4,5-diphenyloxazole; thiazole derivatives such as Z-p-dialkylaminophenyl-methyl-benzthiazole; as also the following:

Oxazoles and imidazoles described in German patent application K 35,586 Iva/57b, filed Aug. 22, 1958. Acylhydrazones described in German patent application K 36,517 IVa/57b, filed Dec. 19, 1958.

2,2,4-triazines described in German patent application K 36,651 Iva/57b, filed Jan. 7, 1959.

Metal compounds of mercapto-benzthiazole, mercaptobenzoxazole and mercapto-benzimidazole described in German patent application K 37,508 Iva/57b, filed Apr. 18, 1959.

Imidazoles described in German patent application K 37,435 Iva/57b, filed Apr. 9, 1959.

Triphenyiamines described in German patent application K 37,436 IVa/57b, filed Apr. 9', 1959.

Furans, thiophenes and pyrroles described in German patent application K 37,423 Iva/57b, filed Apr. 8, 1959.

Amino compounds with multinuclear heteroc'yclic and multinuclear aromatic ring system described in Gerrlngasn patent application K 37,437 IVa/57b, filed Apr. 9,

Azomethines described in German patent application K 29,270 Iva/57b, filed July 4, 1956.

Molecule complexes are defined in H.v A. Staabs Einfuhrung in die theoretische organische Chemie" (Introduction to Theoretical Organic Chemistry), Verlag Chemie, 1959, pp. 694-707, and by L. I. Andrews, Chemical Review, vol. 54, 1954, pp. 713-777. In particular, the donor/ acceptor complex (qr-complexes) and charge-transfer complexes which are formed from an electron-acceptor and an electron-donor are included. In the present case, the photoconductors are the electrondonors and the substances here called activatorsto distinguish them from the dyestutf sensitizers-'arc the electron-acceptors. The electron-donors have a low ionization energy and have a tendency to give up electrons. They are bases in the senselof the definition of acids and bases given by G. N. Lewis (H. A. Staab, as above, p. 600). The electron-donors primarily concerned in the present case are the photoconductors described above; These photoconductors consist of aromatic or heterocyclic systems containing a plurality of fused rings, or, alternatively, single rings having substituents which facilitate further electrophilic substitution of the aromatic ring, socalled electron-repellent snbstitnents, as described by L. F. and M. Fieser, Lehrbuch der organischen Chemie" (Textbook of Organic Chemistry), Verlag Chemie, 1954, p. 651, Table I. These are, in particular, saturated groups, e.g., alkyl groups such as methyl, ethyl, and propyl; alkoxy groups such as methoxy, ethoxy and propoxy; carbalkoxy groups such as carbmethoxy, carbethoxy and carbpropoxy; hydroxyl groups, amino groups 3 and dialkylamino groups such as dimethylamino, diethylamino and dipropylamino.

The activators in accordance with the invention, which are electron-acceptors, are compounds with a high electron-affinity and have a tendency to take up electrons. They are acids in the sense of Lewis definition. Such properties are possessed by substances'having strongly polarizing residues or groupings such as cyano and nitro groups, halogens such as fluorine, chlorine, bromine and iodine; keto'ne groups, ester groups, acid anhydride groups, acid groups such as carboxyl groups or the quinone grouping. Strongly polarizing electron-attract ing groups of this type are described by L. F. and M. Fieser in the Lehrbuch der organischen Chemie, Verlag Chemie, 1954, p. 651, Table I. Of these substances with a melting point above room temperature (25 C.) are preferable, i.e. solid substances, because these impart a particularly long shelf life to the photoconductive coatings as a result of their low vvapor pressure. Substances which are rather deeply colored such as quinones can be used, but those that'are colorless or only weak in color are preferable. Their absorption maximum should preferably be in the ultra-violet region of the spectrum, i.e. below 4,500 A. Further, the activator substances in accordance with the present process should be of lower molecular weight, i.e. between about 50 and 5000, preferably between about 100 and 1000, because with activators of lower molecular weight it is possible for reproducibleresults to be obtained insofar as sensitivity is concerned. Also, the sensitivity remains constant over rather long periods, since substances of lower molecular weight, unlike those of high molecular weight, undergo hardly any change during storage. The

following are examples of such substances:

2-bromo-5-nitro-benzoic acid. 2-br0n1obenzoic acid 2,4-dichloro-benzisatin -l--- 2,6-dichloro-benzaldehyde Hexabromonaphthalic anhydridebz-l-cyano-benzanthrone Cyan acetic acid 2-cyanccinnamic acid 1,5-dicyanonaphthalene- 3,5-dinitrobenzoic acid- 3,5-dinitrosalicylic acid 2,4-dinitro-1-benzoic 8C1 2,4-dinitro-l-toluenefi-suliomc acid- 2,6-dipitro-l-phenol-i-sulphonic aci l,3-dinitro-benzene 4,4-dinitro-biphenyl 3-nitro4-methoxy-benzoic aci knitro-l-methyl-benzoic acid c-nitroA-methyl-1-phenol-2-su1- phonic acid. 2-nitr0benzenesul him'c acid o-Chloronitrobenzene. Chloracetophenone. 2-chlorocinnamic acid.

2-chloro-4-nitro-Lbenzolc acid. 2-chloro-5-nitro-l-benzoie acid. 8-chl0ro-6-nitro-1-benzoic acid.

Mucochloric acid. Mucobromic acid. Styrenedibromide. Tetrabromo xylene.

fl-Trichlorolactic acid nitrile.

Triphenylchlorornethane. Tetrachlorophthalic acid. Tetrabromophthalic acid. Tetraiodophthalic acid. Tetrachlorophthalic anhydride. Tetrabrcmophthalic anhydride. Tetraiodophthalic anhydride. Tetraehlorophthalic acid monoethylester. Tetrabromophthalic acid monoethylester. Tetraiodophthalic acid monoethylester. Iodoform. Fumaric acid dinitrile. Tetracyanethylene. s-Tricyano-benzene.

2,4dinitro-l-chloronaphthalene. 1,4dinitro-naphtha-lene. 1,5-dinitro-naphthalene. 1,8-dinitro-naphthalene. 2-nitrobenzoic acid.

tinitrobenzoic acid. 4-nitrobenzoic acid. 3-nitro-4-ethoxy-benzoic acid. 3-nitr0-2-cresol5-sulphonic acid. 5-nitrobarbituric acid.

4-nitro-acenaphthene.

3-nitro-2-hydroxy -1-benzoic acid--- 4-nitro-benzaldehyde. 2-11itro-1-phenol-4sulphonic acid--- 4-m'tro-phenol. B-nitro-N-butyl-carbazole Picryl chloride.

A-nitrobiphenyl 2,4,7-trinitro-fluorenone. 'Ietranitrofluorenone s-Trinitro-benzene. 2,4,6-trinitro-anisole.

Anthraquinone 1-chl0ro-2-methyl-anthraquinone. Anthraquinone-2-carboxylic acid Duroquinone. Anthraquinonc-2-aldehyde 2,6-dichloroquinone.

Anthraquinone-2-sulphonic acid anilide.

Antlu'aquinone-2,7-disulphonic aci 1,5-diphenoxy-anthraquiuone.

2,7-dinitro-cnthraquinone.

1,5-dichloro-anthraquinone.

1,4dimethyl-anthraquinone.

Anthraquinone-2,7-disulphonic acid bisanilide. Anthraquinone-2-sulphonic acid dimcthylamide. Acenaphthenequinone 2,5-dichloro-benzoquinone. Anthraquinone-Z-sulphonic acid 2,3-dichloro-naphthoquinone-l,4.

methylamide.

1,5-dichlordahthraquin0ne. l-methylchloro-anthraquinone. Picric acid. 2-methylanthraquiuone. Naphthoquinone-l,2. Naphthoquinone-l,4.

Acenaphthenequinone dichloride- Benzoquinone-l ,4 4-nitr0-1-phenol-2-sulphonic acid- 1,2-benzanthraquinone Bromauil Chloranil Pentacenequinone. l-chlor-anthraquinone- TetraceneflJZ-qumone. Chrysenequinone-.- 1,4-toluqu1none.

Thymoquinone 2,5,7,lo-tetrachloropyrenequinone.

The quantity of the solid, non-resinous, substantially colorless electron-acceptors (activators) which is best incorporated in the photoconductive coating to be sensitized is easily established by simple experiments. The

photoconductive coating containing at least one photoabout 300 moles, preferably from about 1 to about 50 moles of electron-acceptor per 1000 moles of photocon ductor. Alternatively, it has also been found that in the photoconductive coatings containing at least one photoconductor and at least one solid, non-resinous, substan1 tially colorless electron-acceptor, it is also very useful to have present the photoconductor and the electron-acceptor in proportions ranging from substantially less than equal amounts to a substantial excess of the electronacceptor with respect to the photoconductor. These proportions in which minor amounts of the photoconductor are added to the activator vary according to the substance used; however, in general, amounts from about 1 0.1 to about 300 moles, preferably from aboutzl to about 50 moles photoconductor per 1000 moles activator.

are used. In some cases, it is also possible to use more than 300 moles photoconductor or activator per 1000 moles activator or photoconductor, respectively, but by exceeding the above range the dark decay of the mixture usually increases, and in such cases coatings made; therefrom are inferior.

Mixtures of several photoconductors and activator substances may also be used. Moreover, in addition to these substances, sensitizing dyestuffs may be added.

By means of the present process, photoconductor contings can be prepared which have a high degree of light sensitivity, particularly in the ultra-violet region, and which are practically colorless. There is the further possibility of the photoconductor coatings being thereby strongly activated in the ultra-violet region and afterwards being invested with a high degree of sensitivity to visible light by a very small addition of dyestufi conductors, to activators, photoconductive mixtures are obtained which have photoconductivity much higher than could be expected from the amount of the photoconductor added to the activator. photoconductivity may be obtained by the addition of dyestuff sensitizers in the same amounts as in the photoconductor-activator mixtures in which the photoconductor 1 is present in a major amount.

A further increase in'the The coatings are treated in other respects in accordance with the known processes of electrophotography, i.e. the photoconductor substances are used in the form of thin, coherent homogeneous coatings on a supporting material. The materials used as supports are primarily metals, such as aluminum, zinc, and copper; cellulose products, such as paper and cellulose hydrate; plastics, such as polyvinyl alcohol, polyamides, and polyurethanes. Other plastics, such ascellulose acetate and cellulose butyrate, especially in a partially saponified form, polyesters, polycarbonates, and polyolefins, if they are covered with an electroconductive layer or if they are converted into materials which have the above-mentioned specific conductivity, e.g. by chemical treatment or by introduction of materials which render them electrically conductive, can also be used, as well as glass plates. In general, materials are suitable the specific resistance of which is less than ohm-cm., preferably less than 10 ohm-cm.

If paper is used as the supporting material, it is preferably pretreated against the penetration of coating solutions, e.g., it can be treated with a solution of methyl cellulose or polyvinyl alcohol in water or with a solution of an interpolymer of acrylic acid methyl ester and acrylonitrile in a mixture of acetone and methylethyl ketone, or with solutions of polyamides in aqueous alcohols or with dispersions of such substances.

For the preparation of the electrophotographic material, the photoconductive compounds are preferably dissolved in organic solvents such as benzene, acetone, methylene chloride or ethyleneglycol monomethylether or other organic solvents or in mixtures of such solvents, and resins and the activatorsand possibly also the dyestulf sensitizersare advantageously added thereto. These solutions are coated upon the supporting material in the normal manner, e.g., by immersion processes, painting or roller application or by spraying. The material is then heated so that the solvent will be removed.

A number of the compounds in question can be applied together to the supporting material or the compounds can be applied in association with other photoconductive substances.

Further, it is often advantageous for the photoconductor substances to be applied to the supporting material in association with one or more binders, e.g., resins. Resins primarily of interest as additions to the photoconductor coatings include natural resins such as balsam resins, colophony and shellac, synthetic resins such as coumarone resins and indene resins, processed natural substances such as cellulose ethers; polymers such as vinyl polymers, e.g. polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl acetals, polyvinyl alcohol, polyvinyl ethers, polyacrylic and polymethacrylic acid esters, isobuty-lene and chlorinated rubber.

If the photoconductive compounds in accordance with the invention are used in association with the resins described above, the proportion of resin to photoconductor substance can vary very greatly. Mixtures of from two parts of resin and one part of photoconductor substance to two parts of photoconductor substance and one part of resin are .to be preferred. Mixtures of the two substances in equal parts by weight are particularly favorable.

For the displacement of sensitivity from the ultra-violet to the visible range of the spectrum, dyestutf sensitizers can be used in addition to the activators. Even very small additions of sensitizer, e.g., less than 0.01 percent, give good results. In general, however, 0.01 to 5 percent, and preferably 0.1 to 3 percent of dyestuif sensitizer is added to the photoconductor coatings. The addition of larger quantities is possible but in general is not accompanied by any considerable increase in sensitivity.

Some examples are given below of dyestulf sensitizers which may be used with good results, and some with very good results. They are taken from Schultz Farbstoiftabellen (7th edition, 1931, 1st vol.):

Triarylmethane dyestuffs such as Brilliant Green (No. 760, p. 314), Victoria Blue B (No. 822, p. 347), Methyl Violet (No. 783, p. 327), Crystal Violet (No. 785, p. 329), Acid Violet 6B (No. 831, p. 351); xanthene dyestufis, namely rhodamines, such as Rhodamine B (No. 864, p. 365), Rhodamine 6G (No. 866, p. 366), Rhodamine G Extra (No. 865, p. 366), Sulphorhodamine B (No. 863, p. 364) and Fast Acid Eosin G (No. 870, p. 368), as also phthaleins such as Eosin S (No. 883, p. 375), Eosin A (No. 881, p. 374), Erythr-osin (No. 886, p. 376), Phloxin (No. 890, p. 378), Bengal Rose (No. 889, p. 378), and Fluorescein (No. 880, p. 373); thiazine dyestuffs such as Methylene Blue (No. 1038, p. 449); acridine dyestuffs such as Acridine Yellow (No. 901, p. 383), Acridine Orange (No. 908, p. 387) and Trypaflavine (No. 906, p. 386); quinoline dyestuflFs such as Pinacyanol (No. 924, p. 396) and Cryptocyanine (No. 927, p. 397); cyanine dyestuffs, e.g., Cyanine (No. 921, p. 394) and chlorophyll.

For the production of copies with the electrocopying material, the photoconductive coating is charged by means of, for example, a corona discharge with a charging apparatus maintained at 6000-7000 volts. The electro-copying material is then exposed to light in contact with a master. Alternatively, an episcopic or diascopic image is projected thereon. An electrostatic image corresponding to the master is thus produced on the material. This invisible image is developed by contact with a developer consisting of carrier and toner. The carriers used may be, for example, tiny glass balls, iron powder or tiny plastic balls. The. toner consists of a resin-carbon black mixture or a pigmented resin. The toner is used in a grain size of 1 to The developer may also consist of a resin or pigment suspended in a non-conductive liquid in which resins may be dissolved. The image that is made visible by development is then fixed, e.g., by heating with an infra-red radiator to 100-170 0., preferably 150 C. or by treatment with solvents such as trichloroethylene, carbon tetrachloride or ethyl alcohol, or steam. Images corresponding to the master characterized by good contrast effect are obtained.

If transparent supporting material is used, the electrophotographic images can also be used as masters for the production of further copies on any type of light-sensitive sheets.

If translucent supports are used for photoconductive layers such as are provided by the invention, reflex images can be produced also.

The application of the activators in accordance with the present process is not restricted to electrophotographic coatings, but can extend to other devices containing photoconductors, e.g., photoelectric cells, photoresistances, sensing heads or camera tubes and electroluminescent apparatus.

The invention will be further illustrated by reference to the following specific examples:

EXAMPLE 1 A solution containing 26 parts by weight of polyvinyl acetate (e.g., Mowil-ith 50), 25.6 parts by weight of naphthalene, 0.0415 part by weight of 2,3,7-trinitrofluorenone and 800 parts by volume of toluene is ap lied by means of a coating device to an aluminum foil. After the coating has dried, direct images are produced thereon by the electrophotographic process in the following manner: the coated foil is given a negative electric charge by corona discharge, exposed behind a master to the light of a high-pressure mercury vapor lamp watts, at a distance of 30 cm.) for about 10 seconds and then dusted over with a developer.

The developer consists of tiny glass balls and a mixture of resin and carbon black which has been melted together and then finely divided. A developer of this sort con-. sists of, e.g., 100 parts by weight of tiny glass balls (grain size: 100-400 approx.) and a toner (grain size: 20-50,u

7 approx). The toner is prepared by melting together 30 parts by weight of Polystyrol LG, 30 parts by weight of modified maleic acid resin (Beckacite K 105) and 3 parts by weight of Peerless Black Russ 552. The melt 8 EXAMPLE 5 A solution of 26 parts by weight of polyvinyl acetate, 21.6 parts by weight of'1,5-diethoxynaphthalene and 0.258 part by weight of 1,2-benzanthraquinone in 800 is then grgund and screened. The finely g g 'i 'f gf 9 5 parts by volume of toluene is applied to paper and the hares to t 6 Parts f the coat ng not z g yt b unna material is further processed as described in Example 1. l exposmie i a Posmve Image t e mas er ecomes The exposure time (l25-watt high-pressure mercury vapor visible. It is slightly heated and thereby fixed. lamp) is 20 seconds If 2 3 8 ofluorenone 15 not addeg to h f'fi Without the 1,2-benzanthraquinone addition, the copy descn ed a even an f? of WO es W1 0 still has considerable. background after an exposure of 80 not produce an electrophotographrc image. Seconds EXAMPLE 2 EXAMPLE 6 26 parts by weight of polyvinyl acetate, 16.6 parts by 6 parts by Weight of polyvinyl acetate, 17.8 parts weight of fluorene and 0.3602 part by weight of tetranitro- 15 by s of Phenanthrene and 9- Part by Welght of fluorenone are dissolved in 800 Parts by Volume of t01u chloranil are dissolved together 1n 800 parts vby volume ene. This solution is applied to an aluminum foil and of toluenesolutlqn aPphed to a superficlally further procedure is as described in Example 1. Expo- Toughened alummum 9 f then the matenal 1 Sure time if a 125 watt higbpressure mercury vapor lamp thenprocessed as described in Example 1. Ifthe mateis used is seconds rial is exposed to a 125-watt high-pressure mercury vapor Without the tetranitrofluorenone addition, the images lamp an eXPOSm'ePf 9 seconds glves an Image free of obtained even after an exposure of two minutes are background and rich in contrast, whereas without 'the free of background, i.e., the exposed parts are not fully chloraml addition there is heavy background even after discharged and therefore retain a certain amount of dean exposure of one mmuteveloper; 7 EXAMPLE 7 EXAMPLE 3 A solution containing 26 parts by weight of polyvinyl A solution of 26 parts by Weight of polyvinyl acetate, acetate, 24.4 parts by weight of o-dianisidine and 0.0256 17.8 parts by weight of anthracene and 0.3357 part by part by Weight of dibromomaleic anhydride in 800 parts i h f hexabrornonaphthalic anhydride in 800 parts by volume of toluene is applied to an aluminum foil and by volume of toluene is applied to aluminum and further 30 the material is further processed as described in Examprocedure isas described in Example 1. With a 125-watt ple 1. The exposure time (125-watt high-pressure merhigh-pressure mercury vapor lamp, the exposure time is cury vapor lamp) is 2 seconds. Without the dibromo- 4 seconds. maleic anhydride addition, it is 10 seconds.

TABLE A No. A B O D E 1 Polyvinylacetate, 10 parts (1) 8 120 see. (b) (ca.). 2 rin 8 Anthrnquinone, 0.08 30 see. (b). 8 Anthraqmuone, 0.17 20 see. (b). 8 Anthraquinone, 0. 5 20 see. (b). -8 see. (b). 8 60 see. (b). 8 60 sec. (b). 8 90sec. (b). 8 u 90sec. (b). 8 Anthraqulnone, 0.17 20 see. (b). 8 dr\ 20sec. (b). 8 .dfl 20 see. (b). 3 240 see. (a). (in 8 Anthraqumone, 0 25 180 see. (a). Cyclized rubber, 10 parts (2) 8 b 240 see. (a). rin 8 Anthraquinone, 0.25 30 see. (a). Atterchlorinated polyvinylchlorideflparts (3) S 10 see. (a Polyvinyleliloride, nfterehlorinated, 7parts (3). 8 Anthraquinone, 0.25 part- 3 see. (a), Maleic acid resin, 10 parts (4) 8 240 see. (a). rln 8 Anthraqumone, 0.25 part; 60 see. (a). Chlorinated rubber, 10 parts (5) 8 0 $00. (a). d 8 Anthraquinone, 0.25 part- 10 see. (a), Chlorinated rubber, 10 parts (6) 8 20 see. (a). rln 8 Anthraquinonc, 0.25 10 see. (a).

8 1,2-beuzanthraquinone, 0.31 part 1-1.5 sec. (a). 8 Hexabrornonaphthalic anhydride, 0.80 part 11.5 see. (a). 8 23,5,7-tetranitrofluorenone, 0.43 part 1.5 see. (a). 8 Drbromomaleic anhydride, 0.30 part... 4-6 see. (a). 8 Nitrgiterephthalic acid-dimethylester, 0.28 6-8 see. (a).

pa 8 Tetracyano ethylene, 0.15 part 4-6 see. (a). 8 1,3,5-trinitrobcnzene, 0.25 part 1.5-2 see. (a).

Without the hexabromonaphthalic anhydride addition, an exposure of as much as 30 seconds gives an image which contains background.

EXAMPLE 4 Explanations ori Table A Column A: Quantity and kind of binder used. -In all cases, the quantities stated were dissolved in 200 parts by volume of toluene.

Column B: Quantity of the photoconductor; In all examples, the same amount of pyrene was used. Column C: Quantity of the activator used. Column D: Quantity of dyestuff sensitizer used (Rhov damine B extra).

Column E: Time of exposure, using:

(a) a 250 watt photographic lamp (Philips Photocrescenta). (b) a customary watt incandescent lamp.

9 The tests were carried through under the same experi mental conditions, with the exception of the variations stated in the table.

1) The polyvinyl acetate used was the product commercially available under the registered trademark Mowilith C.

(2) The cyclized rubber used 'was the product commercially available under the registered trademark Pliolite S-SD.

(3) The afterchlorinated polyvinylchloride used was the product commercially available under the registered trademark Rhenoflex.

(4) The maleic acid resin used was the product commercially available under the designation Alrosat.

(5) The chlorinated rubber used in Table A, col. A, under N0. 21 (5) was the product commercially available under the registered trademark Parlon S-5 cps.

(6) The chlorinated rubber used in Table A, col. A, under N0. 23 (6) was a product commercially available under the registered trademark Pergut 8-40.

The following Table B shows further examples of various photoconductors which were activated, and the reduction in exposure time caused by the activators:

TABLE B A B G 26 Chloranil Hexabromonaphthalic anhydride 2,4,5,7-tetranitr0fluorenone Haggromonaphthalic anhy- 13.6 hydroquiuonedimethy1ether.*

25.6 naphthalene 2,4,5,7-tetranitrofluorenone 1,5-dinitronaphthalene 1,4-benzoquin0ne Ohloranil 3,5-dinit-rosalicylic acid Dibromomaleic anhydride Tetrachlorophthalic anhydride Hexabromonaphthalic anhydride Pierylchloride 2,4,5,7-tetranitrofluorenone Chloranjl 1,2-benzanthraquinone Dibromomaleic anhydride Hexabromonaphthalic auhydrid Picrylchloride 1,5-diethoxynaphthalene.

15.4 acenaphthene 26 15.2 acenaphthyleue-- 26 Hexabromonaphthahc anhydnde.

2,4,5,7-te tramtrofluorenone 15.4 diphenyl 18 1,2-benzanthraquinone. Tetrachlorophthalic anhydr Picrylchloride 2,4,5,7tetranitrofluorenon Chloranil 1,2-benzanthraquinon Tetraehlorophthalic anhydn Hexabromonaphthalic anhydride Picrylchloride 24.4 o-dianisidine 16.6 fluorene 26 1,2-benzanthraquinon Hexabromonaphthalic Picrylchlorlde 3,5-dinitrosalicylic aei 1,2-benzanthraquinon Dibromomaleic anhydri Tetrachlorophthalic anhydr 2,4,5,7-tetranitrofluorenone 17.8 wthracene 26 22.8 chrysene 52 1,2-benzanthraouinoue- Tetrachlorophthaltc anhydn Hexabromonaphthalic anhydride Picrylchloride 2,4,5.7-tetranitrofluorenone Benzoquinone Chloranil 2,4,5,7-tetranitrotluoreno 1,4-benzoquinone Chloranil 3,5dinitrosalicylic ac 1.2-benzanthraquinone- Dibromomaleic acid anhy r1 8. Tetrachlorophthalic anhydride-.. Hexabromonaphthalic anhydride Picrylehloride 2,4,5.7-tetranitrofluorenone. 1.2-benzanthraquinone- Dibromomaleic anhydride. Tetrachlorophthalic anhydr1de.-- Hexabromonaphthalic anhydride Picrylchloride 2,4,5,7-tetranitrofluorenone 16.9 diphenylamlne 26 26.9 2,2-dinaphthylamine 26 17.8 phenanthrene 26 TABLE BContinued A B C D 19.3 2-phenyl-indole 26 Chloranil $4 1,2-b enz anthraquinone. $4

Dibromornaleic anhydride. $4

Tetrachlorophthalie anhydride )4 Hexabromonaphthalic anhydride. }4

Picrylchloride 2,4,5,7-tetranitrofluorenone- 16.7 carbazole 26 Chloranil Mo 1,2-benzanthraquiuone- M n 3,5-dinitrosa1icy1ic acid 93 Dibromomaleic anhydride M o Tetrachlorophthalic anhydride )8 Hexabromonaphthalic anhydride- Ho Picrylchloride 2,4,5,7-tetranitrofluorenone Mu 19.9 thi0diphenylamine 26 l,2-benzanthraquinone )6 25.48 2,4bis-(4-diethyl- 26 2,4,5,7-tetranitrofluorenone- Mo aminopheny1)-1,3,4- 1,2-benzanthraquinone. M o oxadiazole. 2,4-dichlorobenzoic acid. Mo Tetrachlorophthalic acid- $20 18.2 2,4-bis-(4-diethyl- 18 3,5Fdinit-rosalicylic acid H o aminophenyl) -1,3,4- 1,2-benzanthraquinone $6 triazole. Dibromomaleic anhydride $6 Hexabromonaphthalic anhydride- )o Picrylchloride ,40 2,4,5,7-tetranitrofluorenone lo Explanations on Table B The table describes a series of experiments carried through for improving the photoconductivity of organic substances by adding activators.

In Column A the quantity and nature of the substance used is stated. The substances marked with a yielded no electrophotographic images even after an exposure time of several minutes.

In Column B the quantity of the binder used is stated. In all of the cases, polyvinyl acetate having a K-value of 50 was used. Binder, photoconductive substance, and activator were dissolved in toluene, coated onto an aluminum foil, and dried.

In Column C the substance used as activator is stated. In all of the cases 1 mol of the activator stated under C was used per moles-of the substance stated under A.

In Column D the reduced time of exposure is stated which is required to produce images equal in quality to those produced without the addition of an activator. In those cases where a prolonged exposure of the photoconductor yielded not even a weak image (marked with a the calculation of the reduced time of exposure was based on the longest exposure used for the unactivated photoconductor substance.

Alternatively, the increase in sensibility obtained by the addition of activating substances may be taken from a comparison of the degrees of blackening obtained with the activated photoconductive layer and with the unactivated photoconductive layer, under the same customary step wedge (e.g. Kodak No. 2 density strip with color patches).

EXAMPLE 8 A solution containing 20 parts by weight of afterchlorinated polyvinyl chloride with a content of chlorine from 61.7 to 62.3 percent and K-value from 59 to 62, 18.01 parts by weight of 2,4,5,7-tetranitrofluorenone and 0.216 part by weight of 1,5-diethoxynaphthalene dissolved in a mixture of 450 parts by volume toluene and parts by volume butanone is applied to an aluminum foil. The subsequent procedure is that described in Example 1. The exposure time, with a 100 watt incandescent lamp at a distance of 30 centimeters is 2 seconds.

Without the addition of 1,5-diethoxynaphthalene the exposure time is about 40 seconds.

11 In the following table, the exposure times are given, which were obtained when using other photoconductors instead of the 1,5 -diethoxynaphthalene.

Exposure time A solution of 12 parts by weight of chlorinated rubber (Pergut 8-40), 5.04 parts by weight of 1,3-dinitrobenzone and 0.106 part by weight of anthracene in 150 parts by volume of toluene is applied to a paper foil and the material is further processed as described in Example 1. The exposure time (125 watt high pressure mercury vapor lamp) is 20 seconds. Without the anthracene addition, even after an exposure time of 80 seconds, only traces of an image were obtained. This means that the exposed parts of the coating were not discharged and therefore still attracted developer.

In the following table the exposure times are given, which were obtained, when using other photoconductors instead of the 1,3-dinitrobenzene.

Exposure time (seconds) Photoconductors (parts by weight):

2,2'-dinaphthylamine (0.180) 2,5-bis-(4'-diethylaminophenyl)-1,3,4 oxdiazole EXAMPLE 10 A solution containing 20 parts by weight of the afterchlorinated polyvinyl chloride mentioned in Example 8, 21.02 parts by weight of benzile and 0.370 part by weight of benzidine in a mixture of 450 parts by volume of toluene and 150 parts by volume of butanone is applied to an aluminum foil and the material is further processed as described in Example 1. The exposure time (125 Watt high pressure mercury vapor lamp at a distance of 30 centimeters) is 10 seconds. Without the addition of the benzidine activator, even after an exposure time of 4 minutes, no electrophotographic image could be obtained.

In the following table, the exposure times are given which were obtained when using photoconductors other than benzidine.-

Exposure time Photoconductors (parts by weight): (seconds) 2,2'-dinaphthylamine (0.540) 20 2,5-bis-(4'-diethylamino-phenyl) 1,3,4 oxdiazole (0.730) Poly-N-vinylcarbazole (0.390) 30 EXAMPLE 11 A solution containing 6.2 parts by weight of afterchlorinated polyvinyl chloride, 3.94 parts by weight of 1,5-dichloronaphthalene and 0.145 part by weight of 2,5-bis- (4'-diethylaminophenyl)-l,3,4-oxdiazole in a mixture of 135 parts by volume of toluene and 45 parts by volume of butanone is applied to a paper base and is further processed as described in Example 1. The exposure time (125 watt high pressure mercury vapor lamp at a distance of 30 centimeters) is seconds. Without the addition of the oxdiazole compound, even after an exposure time of 40 seconds, no image could be obtained. When the oxdiazole compound is replaced by 0.120 part'by weight of 12 2,2'-dinaphthylamine, the exposure time is about 10 seconds.

EXAMPLE 12 To a solution containing 28.6 parts by weight of tetra-.

chlorophthalic acid anhydride and parts by weight of afterchlorinated polyvinyl chloride in a mixture of 150- parts by volume of butanone and 450 parts by volume of toluene, X parts by weight of photoconductor and Y parts by weight of dyestutf sensitizer are added. In the following table, the amounts of the photoconductor and sensitizer are given together with the corresponding exposure times. It is advantageous to dissolve the dyestutf Photoconductor X parts DyestutI sensitizer Y Exposure by weight Parts by weight ime (Seconds) ca. 200 .do 9 o 0.30 Rhodamine B extra 2-3 0.54 2,2-dinaphthylamine one 4-5 Do 0.30 Rhodamine B extra..-" 2 0.73 2,5-bis-(4-diethylamino- None 4 phenyl)-1,3,4-oxdiazole.

Do 0.30 Rhodamine B extra 1-2 Do 0.025 Basischreinblau 3 G- 2 Do 0.015 Bri11antgreen extra.-." 3 Do 0.015 Kristallviolet--. 2 Do 0.015'Methylenblue 0. 5 0.39 poly-N-viuylcarbazole- 0.30 Rhodamine B ext 9 Do None 20 EXAMPLE 13 A solution is prepared, containing 57.2 parts by weight of tetrachlorophthalic acid anhydride and 65 parts by weight of afterchlorinated polyvinyl chloride in 700 parts by volume toluene andsufiicient butanone is added to make up 1000 parts by volume. To 50 parts by volume of the resulting stock solution, one of the photoconduc tors listed below is added, and the solution is applied to an aluminum foil and further processed as described in Example 1. In the following table, the added photocondu'ctors are indicated, and the corresponding exposure times are given. pressure mercury vapor lamp in a distance of about 30 centimeters from the exposedmaterial was used in all instances.

Exposure time.

1 Image with heavy background,

As the light source, a -watt high 13 Photoconductor (parts by weight) Exposure time Continued (seconds) Phenanthrene (0.089) 60 Phenoxathin (0.100) 10 Stilbene (0.090) 30 2,3,5-triphenylpyrrole (0.153) l 1,l'-dinaphthylamine (0.134) 30 1,2'-dinaphthylarnine (0.134) 30 '-tolyl-1-naphthylamine (0.116) 60 Z-phenylindole (0.096) 60 Acenaphtheue (0.077) 60 Diphenyl (0.077) 120 N-methyldiphenylamine (0.091) 30 4-hydroxy-diphenylamine (0.092) 30 Phlorglucinediethyl ether (0.091) 120 EXAMPLE 14 57.2 parts by weight of tetrachlorophthalic acid anhydride and 65 parts by weight of polyvinyl acetate are dissolved in sufiicient toluene to make up 1000 parts by volume. To 50 parts by volume of this stock solution, one of the photoconductors listed below is added and the coating solution is applied to an aluminum foil and further processed as described in Example 1. The light source and the distance of the light source from the exposed material were the same as in the foregoing example.

Exposure time Photoconductor (parts by weight) (seconds) None 60 Naphthalene (0.064) 10 Hydroquinonedimethyl ether (0.069) N-ethylcarbazole (0.097) Anthracene (0.089) Carbazole (0.081) Chrysene (0.114) Pyreue (0.101) o-Dianisidine (0.122) 1,5-diethoxynaphthalene (0.101) 2,6-dirnethyl-naphthalene (0.078) Hexamethylbenzene (0.081) 2,2-dinaphthylamine (0.134) Diphenylamine (0.084) Diphenyleneoxide (0.084) Indole (0.058) Fluorene (0.083) Stilbene (0.090)

EXAMPLE 15 29.62 parts by weight of phthalic acid anhydride and 33 parts by weight of afterchlorinated polyvinyl chloride are dissolved in 670 parts by volume of toluene and 330 parts by volume of butanone. To 50 parts by volume of the resulting stock solution, one of the photoconductors listed in the following table is added; these coating solutions are applied to an aluminum foil, and further processed as described in Example 1. The light source and the distance of the light source were the same as in Example 13.

Exposure time Photoconductor (parts by weight): (seconds) None 1 60 N-ethylcarbazole (0.10) 5 Anthracene (0.09) Chrysene (0.114) Pyrene (0.10) 10 2,2'-dinaphthylamine (0.134) 10 2,3,5-triphenylpyrrole (0.153) 10 1 No image obtained,

EXAMPLE 16 49.2 parts by weight of chloranil and 56 parts by weight at afterchlorinated polyvinyl chloride are dissolved in a mixture of 1170 parts by volume of toluene and parts by volume of butanone. The resulting solution is filled up to 2000 parts by volume with chlorobenzene. To 100 parts by volume of this stock solution, one of the photoconductors listed in the following table is added; the coating solution is applied to an aluminum foil and further processed as described in Example 1. The light source and the distance of the light source were the same as in Example 13.

Exposure time 10.6 parts by weight of 2-acetyl fluorene and 12 parts by weight of afterchlorinated polyvinyl chloride are dissolved in parts of toluene and sutficient butanol to make up 250 parts by volume of solution. To 50 parts by volume of this stock solution, one of the photoconductors of the following table is added. The solution is applied to an aluminum foil and further processed as described in Example 1. The light source and the distance of the light source were the same as in Example 13.

Exposure time Photoconductor (parts by weight): (seconds) None 1 180 o-Dianisidine (0.120) 30 2,5 -bi s- 4'4liethylaminophenyl) -l ,3,4-oxdiazole 1 No image obtained.

EXAMPLE 18 44 parts by weight of 9 acetyl-anthracene and 48 parts by weight of afterchlorinated polyvinyl chloride are dissolved in 700 parts by volume of solution. To 50 parts by volume of the resulting stock solution, one of the photoconductors of the following table is added. This solution is applied to an aluminum foil and further processed as described in Example 1. The light source and the distance thereof was the same as in Example 13.

Exposure time Photoconductor (parts by weight): (seconds) None 1 180 Hydroquinonedimethyl ether (0.069) 30 N-ethyl carbazole (0.097) 60 Anthracene (0.089) 60 Hexamethylbenzene (0.081) 30 1 Image with heavy background.

EXAMPLE 19 46.2 parts by weight of pyrene-3-aldehyde and 50 parts by weight of afterchlorinated polyvinyl chloride are dissolved in 670 parts by volume of toluene and suflicient butanol to make up 1000 parts by volume of solution. To 50 parts by volume of the resulting stock solution one of the photoconductors of the following table is added. The solution is applied to an aluminum foil'and further processed as described in Example 1. The light source and the distance of the light source were the same as in Example 13.

Exposure time Photoconductor (parts by weight): (seconds) None 30 Naphthalene (0.064) 20 Hydroquinonedimethyl ether (0.070) 20 N-ethylcarbazole (0.10) 10 Anthracene (0.090) 20 Chrysene (0.114) 20 Pyrene (0.10) 20 Hexamethylbenzene (0.080) 20 2,2'-dinaphthylamine (0.135) 15 2,5-bis- (4'-diethylaminophenyl -l ,3,4-oxdiazole (0.180) 5 2,3,5 -ttiphenylpyrrole (0. 150) 20 EXAMPLE 20 Photoconductor (parts by weight): (seconds) None 1 180 N-ethylcarbazole (0.10) Anthracene (0.09) 30 o-Dianisidine (0.12) 10 2,5-bis- (4'-diethylaminophenyl) -l ,3 ,4-oxdiazole 1 Image with heavy background.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. A sensitized photoconductive layer comprising a photoconductive 1,3,4-triazole and at least one solid, nonresinous, substantially colorless electron-acceptor.

2. A sensitized photoconductive layer according to claim 1 in which the triazole is a 2,5-bis-(p-aminophenyl)- 1,3,4-triazole.

3. A sensitized photoconductive layer according ,to claim 1 in which the triazoleis 2,4-bis-(4-diethylaminophenyl) -1,3,4-triazole.

4. A sensitized photoconductive layer comprising a photoconductive 1,3,4-triazole and at least one solid, nonresinous, substantially colorless electron-acceptor, the layer containing the photoconductor and the electron-acceptor in proportions ranging from substantially less than equal amounts to a substantial excess of the photoconductor with respect to the electron-acceptor and from substantially less than equal amounts to a substantial excess of the electron-acceptor with respect to the photoconductor.

5. A sensitized photoconductive layer comprising a photoconductive 1,3,4-triazole and at least one solid, nonresinous, substantially colorless electron-acceptor in proportions ranging from about 0.1 to about 300 moles of the electron-acceptor per 1000 moles of photoconductor.

6. A sensitized photoconductive layer comprising a photoconductive 1,3,4-triazole and at least one solid, nonresinous, substantially colorless electron-acceptor in proportions ranging from about 0.1 to about 300 mols of the photoconductor per 1000 moles of the electron-acceptor.

7. A sensitized photoconductive layer comprising a photoconductive 1,3,4-triazole and at least one solid, nonresinous, substantially colorless electron-acceptor in proportions ranging from about 1 to about 50 moles of the electron-acceptor per 1000 moles of the photoconductor.

8. A sensitized photoconductive layer comprising a photoconductive 1,3,4-triazole and at least one solid, nonresinous, substantially colorless electron-acceptor in proportions ranging from about 1 to about 50 moles of the photoconductor per 1000 moles of the electron-acceptor.

9. A layer according to claim 1 in which the electronacceptor is 2,4,7-trinitrofiuorenone.

10. A layer according to claim 1 in which the electronacceptor is tetranitrofluorenone.

11. A layer according to claim 1 in which the electronacce'ptor is hexabromonaphthalic anhydride- 12. A layer according to claim 1 in which the electronacceptor is tetrachlorophthalic anhydride.

13. A layer according to claim 1 in which the electronacceptor is 1,2-benzanthraquinone.

14. A layer according to claim 1 in which the electron: acceptor is chloranil.

15. A layer according to claim 1 in which the electronacceptor is dibromomaleic anhydride.

16. A layer according to claim 1 including a resin.

17. A layer according to claim 1 including a dyestuff serisitizer.

18. A photographic reproduction process which comprises exposing an electrostatically charged, supported, photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a photo conductive 1,3,4-triazole and at least one solid, nonresinous, substantially colorless electron-acceptor.

19. A process according to claim 18 in which the photoconductor is a 2,5-bis-(p-aminophenyl)-l,3,4-triazole.

20. A process according to claim 18 in which the photoconductor is 2,4-bis-(4-diethylaminophenyl)-l,3,4-triazole.

21. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a photoconductive 1,3,4-triazole and at least one solid, non-resinous, substantially colorless electron-acceptor, the layer containing the photoconductor and the electron-acceptor in proportions ranging from substantially less than equal amounts to a substantial excess of the photoconductor with respect to the electron-acceptor and from substantially less than equal amounts of to substantial excess of the electron-acceptor with respect to the photoconductor.

22. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a photoconductive 1,3,4-triazole and at least one solid, non-resinous, substantially colorless electron-acceptor in proportions ranging from about 0.1 to about 300 moles of the electron-acceptor per 1000 moles of photoconductor.

23. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a photoconductive l,3,4-triazole and at least one solid, non-resinous, substantially colorless electron-acceptor in proportions ranging from about 0.1 to about 300 moles of the photoconductor per 1000 moles of the electron-acceptor.

24. A photographic reproduction process which com-.

prises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a photoconductive 1,3,4-triazole and at least one solid, non-resinous, substantially colorless electron-acceptor in proportions ranging from about 1 to about 50 moles of the electron-acceptor per 1000 moles of the photoconductor.

25. A photographic reproduction process which comprises exposing an electrostatically charged, supported photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising a photoconductive 1,3,4-triazole and at least one solid, non-resinous, substantially colorless electron-acceptor in proportions ranging from about 1 to about 50 moles of the photoconductor per 1000 moles of the electron-acceptor.

26. A process according to claim 21 in which the electron-acceptor is 2,4,7-trinitrofluorenone.

27. A process according to claim 21 in which the electron-acceptor is tetranitrofiuorenone.

28. A process according to claim 21 in which electron-acceptor is hexabromonaphthalic anhydride.

29. A process according to claim 21 in which electron-acceptor is tetrachlorophthalic anhydride.

30. A process according to claim 21 in which electron-acceptor is 1,2-benzanthraquinone.

31. A process according to claim 21 in which electron-acceptor is chloranil.

the

the

the

the

32. A process according to claim 21 in which the electron-acceptor is dibrornomaleic anhydride.

33. A process according to claim 21 in which the layer includes a resin.

34. A process according to claim 21 in which the layer includes a dyestuif sensitizer.

References Cited by the Examiner UNITED STATES PATENTS Czekalla et al., Chemical Abstracts 52:4317h (1957). Schneider and Compton et a1.: Journal of Chemical Physics, vol. 25:358, 1075-1076 (1956).

NORMAN G. TORCHIN, Primary Examiner.

C. E. VAN HORN, Assistant Examiner. 

1. A SENSITIZED PHOTOCONDUCTIVE LAYER COMPRISING A PHOTOCONDUCTIVE 1,3,4-TRIAZOLE AND AT LEAST ONE SOLID, NONRESINOUS, SUBSTANTIALLY COLORLESS ELECTRON-ACCEPTOR. 